Purple spots on leaf between veins
My 2 tomato plants have been doing very well so far in one these upside-down planters (not the topsy), and have quite a few large fruit ripening. However I'm just starting to see signs of a purple spotting on a couple of leaves in between the veins. It's only on a few leaves at this point, and the most advanced of these is starting to yellow and die.
I took some pictures and posted them here.
I can't seem to find any pictures that resemble this when I search. Phosphorous deficiency perhaps resembles it, but descriptions say it shows most on the veins and what I'm experiencing is between the veins.
Any ideas what it is, or what to do about it?